This invention relates to closures for fluid conduits, and more particularly to arrangements for sealing joints between cooperating tubular members.
The closure of this invention is particularly suitable for heat exchangers of the hairpin type. Examples of such hairpin type heat exchangers are disclosed in U.S. Pat. Nos. 3,155,404 and 3,377,087.
Hairpin type heat exchangers typically have a plurality of tubes bent in the shape of a U. A tube sheet is provided for the inlet end of the tubes and a second tube sheet is provided for the outlet end of the tubes. Each tube sheet has a plurality of holes and the ends of the tubes are secured in the respective tube sheets. A shell which is also generally U-shaped has an opening at one end to allow the tubes and the tube sheets to slide longitudinally through the straight sections of the shell, until both tube sheets are positioned at their respective inlet and outlet ends of the shell. The tube sheets have a sufficiently small diameter to pass through the longitudinal portions of the shell. A cover is applied over the opening at the end of the shell adjacent the bend in the tubes, so that fluid may be circulated through the interior of the shell in heat exchange relation with fluid flowing through the interior of the tubes.
A terminal member or flange on the shell surrounding the tube sheet is provided with a shoulder in opposition to a corresponding shoulder on the tube sheets and a locking ring is placed between the opposed shoulders to secure the tubes in the shell. A closure member is secured over the end of each of the shell terminal members to conduct the heat transfer fluid into and out of the interior of the tubes adjacent the tube sheets. Typically, a seal is provided to prevent the leakage of fluid around the periphery of the tube sheet.
Although these prior closures are satisfactory for use with tube side pressures as high as 2000 p.s.i.g., the seals would fail if higher fluid pressures were encountered. Typically the seal rings are clamped in place by bolts tightened between bolt flanges. In order to retain the seal rings in place at higher pressures, larger bolts and flanges would be required. The larger bolts and flanges necessarily increase the size and cost of the closure, and there is a practical limit to the setting force that can be applied in this way.
Permanent type seals are unsuitable because the closure must allow periodic inspection and replacement of the tubes. Preferably, the seal arrangement should be capable of being installed quickly and easily.